Hydraulic tappets



Oct. 13, 1959 P. F. BERGMANN, SR 1,

HYDRAULIC TAPPETS Filed Jan. 27, 1958 :Ef'g E VENTOR ATTORNEY United StatcS ParenryQ 2,908,260 HYDRAULIC TAPPETS Paul BergniannySn, North Muskegon, Mich., assignor to Johnson Products Incorporated, Muskegon, Mich., a corporation of Michigan This invention relates to tappets and more particularly to hydraulic tappets for use with internal combustion engines.

The efiicient operation of internal combustion engines requires that the engine valves be opened and closed at specific times in the combustion cycle of the engine. Timing cams are normally used for this purpose. The timing cams are adapted to operatethe engine valves through a valve actuating mechanism which is engaged with the valves. The valve actuating mechanism usually includes several parts each of which is subject to expansion and contraction, under changing engine temperatures, and to wear. Consequently, there is also required to be some means for automatically'compensating for any change in the overallv length of the valve actuating parts. Otherwise the timing pattern set by the cams is not always the samel Hydraulic tappets have been acceptedas a suitable means of compensating for any changesin the effective length of valve actuating mechanism. Such tappets are normally disposed between the timing cam and the ,valve actuating mechanism. When engine temperatures rise and the valve actuating parts expand, the eflective length of the tappet decreases accordingly. When the engine temperatures decrease and the yalve actuating parts contract, or when the parts become worn, the etfective length of the tappet increases-accordingly.

Conventionally known hydraulic tappets operate on the principle of transmitting the energy of the actuating cam through hydraulic fluidtrapped in a chamberbehind a plunger member. During'each revolution of the actuating cam small quantities of hydraulic fluid are permitted to escape from the chamber and the plunger is allow to adjust its-relative position in the tappet body. If there has been an increase in the efiective length of the valve train parts the plunger seeks a position lower 'within the tappet body. If there has been a decrease in the effective length of the valve train parts, or no change,

a plunger return spring will return the plunger to a higher relative position in the tappet body, or to its original position, as the case may be. a p

The escape of hydraulic fluid from the pressure chamber of conventionally known tappets is referred to as leakdown and occurs between the plunger and tappet body walls. Leakdown is controlled solely by the fit of the plunger within the tappet body member. This re quires that the plungers and tappetv body members beprecision machined, carefully sorted, and selectively fitted tof chamber relief valve.

7 2,908,260 Patented Oct. 13, 1959 2 sembly of tappets to include such a feature greatly increases tappet costs.

The hydraulic tappet of this invention is not. dependent upon the control of leakdownbetween the plunger and tappet body members in the .manner of conventionally known tappets. Instead, an oil -sealing member, and a relief are provided within the tappet to control the escape of hydraulic fluid from the pressure chamber space after each stroke. This permits a much larger clearance between the plunger and tappet body members. The larger clearance in turn eliminates the precision machining, sorting and selective assembly operations previously required. There is less chance for operational 'fai-lure resulting from minute particles in the hydraulic fluid being caught in the annular clearance space between the plunger and tappet body members. The proposed seal and valve mechanism is less expensive to provide, more dependable in operation andassures a more precise control of the valve train adjustment.

The particular valve arrangement of this invention is disposed between the plunger member and push rod seat member of a tappet. The valve includes a resilient member seated against an end face of the push rod seat member. The resilient member has a valve seat facing engaging the upper end of the plunger member. The resilient member is exposed to the fluid pressure within the pressure chamber spaces of the tappet; When the fluid prssure is greatenough the resilient member is compressed, separated from the plunger member, and fluidis allowed to escapethe pressure chamber spaces.

, The particular relief valve proposed has other decided advantages. These include means of positively'locating the valve relative to. the push rod seat member ans-a means of sealing against fluid leakage past the valve member.v When the resilient member is under comm-es .sion it is radially expanded into secure engagement with the push rod seat member and into fluid pressure sealing engagement with the tappet body walls.

The disclosed relief valve operates to provide tappet adjustment at a-different time in the engine valve operat ing cycle than is the case with conventional hydraulic tappets. In conventional hydraulic tappets leakdown occurs during the raising and lowering of the tappet on the timing cam. Since the conditions causing leakdown vary during the operation of the tappet the escape of hydraulic fluid permitted must be in accord with the most extreme conditions in order to be assured an adequate adjustment when needed. I Thetappet' of this invention adjusts its length after the engine valve is closed and when the tappet has returned to the base circle of the timing cam. The adjustment is only such; as is required under the conditions at the time of adjustment; which is when the tappet and valve train mechanism are inoperative and the bes measure of the adjustment required can be made. 4 'I-heseand other advantages of the disclosed hydraulic tappetwill be more apparent to those familiarwith 'hydraulic tappets upon a reading of the following specification and'anexamination of the accompanying drawings.

In the drawings: W

Fig. 1 is a cross sectional View of the proposedhydraulic tappet in one operational position.

I Fig. 2 is a cross sectional view of'the same hydraulic tappetin another operational position. t

Fig. 3 is a cross sectional view of the'proposed tappet taken in the plane of line III.--III'in Fig.2 and looking in the direction of the arrows to show the unseated pressure In executing the objects and'purposes'of this invention ahollow tappet body is provided that is closed at one end. a' ho'llow plunger is disposed Within the tappet-body and forms a pressure chamber with the blind 'end of the tappet body. A'push rod seat is received within the tappet body above the plunger. The hollow interior of the plunger forms a hydraulic fluid reservoir. The reservoir of the tappet is in free communication with a source of hydraulic fluid received through passageways formed in the push rod seat and through thetappet'body. A check valve is provided in the lower'end ofthe plunger for admitting hydraulic fluid fromthe reservoir into the pressure chamber when the supply in the'latter falls below operating requirements. The pressure chamber is to be considered as inclusive of the space between the plunger and the tappet body side walls and is 'closed .by a relief valve arrangement provided between the push rod seat and 'the end of the plunger adjacent thereto. The hydraulic fluid pressure in the pressure 'chamber'spa'ces provides an opening force against 'the relief valve to permit the flow of hydraulic fluid from the pressure chamber into the reservoir under certain operating conditions which will'b'e described. 7

Referring specifically to the drawings, the proposed hydraulic tapped 1 includes a tappet body 2 which is reciprocally seated Within a housing 3, such as would be provided by an engine block. The housing :3 has an oil supply passageway 4 communicating with a wide, external and circumferential groove 5 formed about the tappet body 2. T he length of the groove 5 assures communicatiori between the groove and t'he passage 4 as the tappet body reciprocates within the housing. An aperture 6 within groove 5 provides an access for hydraulic fluid into thetappet body.

.The tappet body 2 is closed at one end, which is the end engaged by a timing cam 7, and'is open at the other end. A .plunger 10 is slidably disposed within the tappet body 2. The plunger 10 is hollow and forms a hydraulic fluid reservoir 11. A passage 12 isforrned through the lower end of the plunger to provide a means of communieation between the reservoir 11 and a pressure chamber 13 formed between the end of the plunger and the blind end of the tappet body. A check valve 14 is the presence of hydraulic fluids and related liquid hydrocarbons. A thin metallic annular disc 29 is engaged to one face of the resilient member 28 to provide a better surface for the closing of the valve against the valve seat 26 ofthe plunger. The disc member 29 has a smaller outer diameter and a larger inner diameter than the resilient member 28. Thedisc member is disposed to prevent distortion of the resilient member 28 under high pressure conditions within the pressure chamber 13, which, as willbe explained, are used'to activate the valve.

The valve member .27 is engaged with the push rod seat member 30 which is slidably disposed within the tappet housing above the plunger 10. The rod seat member 30 has a generally spherical depression 31 formed within the upper surface thereof for the reception of the end of a push rod 32 which forms part of the valve train linkage. The peripheral surface of the push rod seat member 30 is formed to provide a sliding and liquid restraining seal with the inner walls of the tappet body 2. An' annular passage or groove 34 is formed about the push rod seat and communicates through the opening 6 in 't'hetappet body and the annular groove 5 with the oil supply passage '4. Passages '36 and 37 formed through the push rod seat member and in communication with groove 34 provides the means of communication for hydraulic fluid to the reservoir 11. Passage 37 extends through the spherical seat 31 as a manufacturing aid in forming the seat. However the passage is sealed against fluid leakage by the engagement of the end of the push rod 32 therein.

The end of the push rod seat 30 next adjacent the plunger is reduced in diameter substantially below that of the internal diameter of the plunger member. This forms a boss 40. An annular groove 41 is provided around the boss and the. compressible valve member 28 is :received in this. groove. The internal diameter of the resilient valve member 28 is smaller than the head portion of the boss 40. Thus, the valve member is-assured biased, by a lightweight spring 15, into closed'position against the end of the plunger and over the passage 12. The check valve 14 prevents communication between the fluid reservoir 11 and the pressure chamber 13 except when the pressure in the reservoir exceeds that in the pressure chamber sufficient to overcome the small tension exertedby the spring 15. I

The lower end of the check valvespring 'IS bears against a cap 16. The cap 16 is engaged to the end of the plunger 10 about wall 19 formed 'on the lower end thereof. An aperture 17 in the terminal end of the cap and apertures 18 provided in the sides thereof permit the flow of hydraulic fluid about the cap. The plunger is biased away from the closedend of the tappet body by a plunger return spring 20.

The fit of the plunger 10 within the tappet body 2 is such that the pressure-charnber 13 is to be considered to extend to the top edge-of the plunger and to be inclusive of the annular :space 21 between the outer walls of the plunger and the inner walls of the tappet body. This clearance is not suflicientto allow an, unrestricted flow .of the hydraulic fluid between the plunger and tappet body walls. However, it is suflicient to permit a'nearuniform fluid pressure condition to be built up between the pressure chamber and about the plunger in the'course of tappet operation. "In a tappet constructed according to this invention, the clearance between the plunger and the inside surface of the tappet body may be as much as .005 or .006 of an inch as compared to the 0.0002- 0;00023 of an inchclearance permissible in'conventional tappets.

The upper end of the plunger 10 is machined to form a smooth and accurate valve seat 26 which cooperates with the-relief valve 27 of this invention to close offthe'end a tight fit thereon. The disc member 29 of the valve will be noted to have .an internal diameter greater than that of the head of the boss 40 thus eliminating interference between the two parts.

The compressible member 28 of the valve 27 is backed by a radially disposed end-wall of the rod seat member 30. Any pressures imposed upon the lower face of valve 27, tending to lift the disc part from the valve seat 26, will compress the valve member 28. This causes the resilient material to flow or expand radially outward and inward, locking'the valve into tighter engagement with the push rod seat member 30 and into tighter sealing engagement with the walls of the tappet body member2 engaged thereby. Separation of the disc member 29 from the v valve seat 26 provides a return or bleed passage for the escape of hydraulic fluid from the pressure chamber 13 back into the reservoir 11 Fig. 2 shows such a passage with the separation highly exaggerated for illustration I scribed is prevented from disassembly from the tappet of the pressure chamber 13 extending about. the-plunger.

body 2 by a snap ring 60 seated in a suitable groove 62 provided in the inner wall of the tappet body 2 adjacent its open end.

Operation For the purposes of describing the operation of this invention, it is assumed that the tappet is in the position illustrated in -Fig. 1 with the eccentric portion of the cam -7 about to be engaged with the lower end of the tappet body. The valve train mechanism has not been-shown because it is considered to'be of such conventional design asto be Ireadily understood and-its relation to parts shown to be adequately known,- without illustration.

The forces within the tappet are substantially in balance. The plunger return spring 20uholds' the plunger engaged'withthe relief valve member 27 and the relief valve 27 against the push rod seat member 30. The push rod 32 is backed by the resistance of the engine valve spring to prevent further upward movement of the push rod seat member. The reservoir chamber 11, pressure chamber 13, and annular pressure chamber space 21 are filled with hydraulic fluid at substantially equal pressures.

When the eccentric portion of cam 7 engages the base 39 of the tappet body 2, the tappet body is lifted. The plunger 10 is also raised due to the incompressible nature of the hydraulic fluid trapped in the pressure chamber 13. The plunger member 10 acts against the relief valve 27 in its effort to lift the push rod seat member 30. The resistance of the engine valve spring to compression is greater than that of the compressible member 28 of the relief valve. Consequently, the member 28'is compressed a few thousandths of an inch in the first effort of the plunger to lift the rod seat member 30.

The compressible member 28 is caused to spread radially and to be forced into more secure engagement with the push rod seat member, within groove 41. The resilient member 28 is also forced into tighter fluid sealing engagement with the internal walls of the tappet body member.

During the remainder of the rise of the tappet body 2, under the influence of the timing cam 7, the push rod seat member 30 transmits the cam lift force to the push rod 32 in the effort to lift the engine valve against the resistance of the engine valve spring.

The increased resistance of the engine valve spring to compression, in allowing the engine valve to. be opened further, produces an increased fluid pressure condition in the pressure chamber 13. The increasing fluid pressure condition in chamber 13 seeks to equalize itself in the annular pressure chamber space 21 about the plunger. However, the restrictive character of the annular space 21 produces a pressure gradient between the upper end of the plunger, near the relief valve, and the lower end thereof, which opens into the pressure chamber space 13.

During the rise of the tappet the pressure build up in chamber 13 will tend to raise the pressure condition in space 21, next adjacent to the relief valve, to the same pressure level. As the tappet passes the crest of the cam 7 and begins to fall back, the resistance of the engine valve spring decreases. The pressure condition in chamber 13 also begins to fall 01f accordingly. During the return of the tappet to the base circle of cam 7 the pressure condition in chamber 13 will fall below that at the upper end of the annular space 21 next adjacent the relief valve 27. p

At the return of the tappet to the base circle of cam 7, the force of the engine valve spring will be withdrawn from the rod seat member 30. This happens when the engine valve closes. The resilient member 28 of the relief valve-27 Will still be compressed, just as it was when the tappet first started its rise and as it remained throughout the rise and fall of the tappet.

At the moment the engine valve spring force is withdrawn from the rod seat member 30 the unit pressure in the pressure chamber space 13 falls off. Accordingly, there exists a greater unit pressure at the upper end of the annular pressure chamber space 21, near the relief valve 27, than exists below the plunger.

.T he unit pressure condition near the upper end of the annular pressure chamber space 21 is suflicient to hold the resilient member 28 compressed as the tappet body member 2 returns to the base circle of the timing cam 7. The plunger 10 travels with the tappet body member 2, on the return to the base circle of the cam, just as it did during the initial rise of the tappet and compression of the resilient member 28 of the relief valve, Thus the greater-pressure condition built up next adjacent the relief valve 27, during the operation of the tappet, and unable to be dissipated as fast as in the pressure chamber space 13, serves to open the relief valve 27.

a When the relief valve 27 opensasmall amount of hydraulic fluid is allowed to escape from the pressure cham-' ber space 21 into the reservoir 11. To the extent that this depletes the supply of hydraulic fluid in the pressure chamber spaces, the plunger member 10 may be axially adjusted within the tappet body member.

If the valve actuating members have increased their length, due toexpansion resulting from increased engine temperature conditions or the like, then the push rod member 30 will have been returned to a lower relative position in the tappet body member 2 before the relief 'valve 27 opened. As a result, the relief valve is permitted to open later and not as wide as if there had been no growth in the valve train parts. However, the opening permitted the valve 27 is sufiicient to take care of the incremental growth of the parts, during one cycle of the tappet operation, and still vent the pressure chamber spaces to the reservoir chamber. .The plunger member 10 will retain its lower position, due to the fluid loss from the pressure chamber spaces, and the necessary adjustment of the tappet will have been made. Y

When the valve train parts have contracted, shortening their effective length, the valve opening occurs sooner. The plunger return spring 20 adjusts the plunger to a higher relative position in the tappet body member, accordingly, and the check valve 14 opens as required to re plenish fluid in the pressure chamber 13 and to balance the condition therein with that in the reservoir 11.

In discussing the operation of the disclosed tappet, it is to be remembered that these tappets operate at high speeds and that the adjustments involved and the fluid exchange to effect the adjustments are all incremental measurements. The disclosed tappets are of an actual size much smaller than is shown by the illustrations and the valve opening, clearance spaces, etc., are required to be exaggerated for illustration purposes. Also, it should be said that while the theory of operation of this tappet is considered to be as has been described, that the tappet may operate differently. .The momentum of the valve train parts, including push rod, push rod seat, and plunger cause an increase in pressure in chamber 13 and space 21 at the instant that downward travel of these parts is stopped by the cam. This pressure would be sufficient to separate relief valve 27 from surface 26 to permit a leakage of fluid from the pressure chamber into the reservoir, thus allowing the plunger to adjust itself to the proper position in readiness for the next opening of the engine valve. However, tests have proven that the results disclosed are obtained by tappets made in accord with the teachings of this invention, both in the disclosed form and with certain modifications.

Therefore, and in conclusion, while a preferred embodiment of this invention has been described it will be understood that other modifications and improvements may be made thereto. Such ofthese modifications and improvements as incorporate the principles of this invention are to be considered as included in the hereinafter appended claims unless these claims by their language expressly state otherwise.

I claim:

1. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers at one end of said plunger; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative to said tappet body, and comprising: having said pressure chamber in restricted communication with the annular space between said plunger and said tappet body, valve means disposed between said pressure and reservoir chambers at the other end of said plunger and including ,a compressible member having a noncompressible facing engaged with said plunger, said compressible member. yielding axially to a fluid pressure within said pressure chamber less than that required'to efiect movement of said push rod seat and greater than that required to actuate said plunger for unseating said facing from said plunger and venting said pressure chamber to said reservoir.

2. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative to said tappet body, and comprising; said pressure chamber being in restricted communication with the annular space between said tappet body and said plunger, a valve member disposed between said push rod seat and plunger member and engaged with the upper end of said plunger for closing said pressure chamber from said reservoir, said valve member including a fluid responsive compressible member engaged against an end wall of said push rod seat and disposed in sealing engagement between the end of said plunger and said tappet body.

3. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative to said tappet body, and comprising; said pressure chamber extending between said tappet body and said plunger to the upper end of said plunger, a valve member disposed between said rod seat and the'upper end of said plunger for closing said pressure chamber, said valve member including a fluid pressure responsive compressible member engaged against an end wall of said push rod seat and having a noncompressible facing seating against the 5 end of said plunger and separating said pressure chamber from said reservoir, said compressible member being disposed in sealing engagement between said push rod seat and tappet body and being axially compressible in response to fluid pressure within said pressure chamber to lift said facing and vent said pressure chamber to said reservoir.

4. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative: to said tappet body, and comprising; said pressure chamber being inclusive of the annular space between said plunger and said tappet body, a valve member disposed between said push rod seat and said plunger for. closing said pressure chamber and separating said reservoir therefrom, said valve member including an' axially and radially compressible member engaged to said push rod seat member adjacent an end wall thereof and disposed in sealing engagement with said tappet'body, said compressible member being responsive to the fluid pressure within said pressure chamber and yielding axially to open said valve and vent said pressure chamber to said reservoir.

'5. In the hydraulic tappet of-claim 4, said push rod seat member having a boss extending from the end face thereof and an annular groove formed therein, said compressible member being annular and having the inner peripheral edge thereof smaller than said push rod seat part and received within said groove.

6. he hydraulic 'tappet'comprising'a blind end hollow tappet body having aplunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative to said tappet body, and comprising; said pressure chamber extending between the peripheral surfaces of said plunger and said tappet body, a valve member disposed between said push rod seat and said plunger and engaging the upper end of said plunger for separating said pressure chamber from said reservoir, said valve member including an axially and radially compressible annular member having one end face thereof engaged with and backed against an end face of said push rod seat member, the inner peripheral edge thereof disposed in sealing engage ment with said push rod seat member, and the outer peripheral edge thereof disposed in sealing engagement with said tappet body, said compressible member yielding axially and separating from said plunger in response to fluid pressure within said pressure chamber to vent said pressure chamber to said reservoir.

7. In a'hydraulic tappet comprising a'blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger relative to said tappet body, and comprising; said pressure chamber extending peripherally about said plunger to the upper end thereof, a valve member disposed between the adjacent ends of said plunger and said push rod seat member and adapted to close and open communication between said pressure and reservoir chambers, said valve member including an axially compressible and radially yielding member engaged against said push rod seat member and disposed in fluid sealing peripheral'engagement with said tappet body and said push rod seat member, said compressible member being responsive to axial pressure imposed by said plunger for yielding radially into fluid pressure sealing engagement with said tappet body and push rod seat member.

8. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers; pressure responsive means for venting said pressure chamber to allow for the axial adjustment of said plunger and push rod members relative to said tappet body, and comprising; said pressure chamber being in restricted communication with the upper end of said plunger, a valve member disposed between the adjacent ends of said plunger and said push rod seat member and for controlling communication between said pressure and reservoir chambers, said valve member including an axially compressible and radially "expansible member backed against an end face of said push rod seat member and disposed in fluid sealing peripheral engagement with said tappet body and said push rod seat member, said compressible member being responsive to axial pressure imposed by said plunger for contracting axially and separating from said plunger to vent said pressure chamber to said reservoir and for expanding radially into fluid pressure sealing engagement with said push rod seat and tappet body to hold such fluid pressure peripheral sealing engagement against fluid pressures in said pressure chamber during the operation of said tappet.

9. In a hydraulic tappet comprising a blind end hollow tappet body having a plunger member slidably disposed therein and forming a pressure chamber with the blind end thereof, a push rod seat member slidably disposed within said tappet body next adjacent said plunger and forming a reservoir chamber therewith, and a reservoir pressure responsive check valve disposed between said pressure and reservoir chambers at one end of said plunger; pressure responsive means for venting said pressure chamber to allow for the axial adjutment of said plunger relative to said tappet body, and comprising: valve means disposed between said pressure and reservoir chambers at the other end of said plunger, said valve means being responsive to fluid pressure conditions within said pressure chamber for venting said pressure chamher to said reservoir, and means provided by said push rod seat member for retaining said valve means engaged therewith.

10. In the hydraulic tappet provided for by claim 9; "said means for retaining said valve member to said push rod seat member comprising a boss formed from the end face of said push rod seat and having an annular groove provided therearound, and said valve means including an inner peripheral portion received and retained in said groove.

References Cited in the file of this patent UNITED STATES PATENTS 2,784,706 Humphreys Mar. 12, 1957 

